A healthy individual's visual perception process begins with the individual's retina(s) receiving stimulation in the form of light. The individual's nerve cells within the retina communicate a signal corresponding to the stimulation to the optic nerve. The optic nerve subsequently transmits a corresponding signal to the visual cortex through the lateral geniculate nucleus. For a vision impaired patient, visual perception may be induced by providing electrical stimulation at one or more of these locations, depending on the nature of the patient's given impairment.
Previous studies have shown that controlled electrical stimulation of the retina induces visual perception in blind patients. A healthy retina has over 100 million photoreceptors. Far fewer, however, are required to restore at least low resolution vision in blind individuals. For example, to enable a blind person to attain unaided mobility and large print reading, two important quality of life indicators, tests have shown that such abilities can be provided. Implants, such as those developed by Second Sight, LLP of Sylmar, Calif., or described, for example, in U.S. Pat. No. 5,935,155 by Humayun et al. and U.S. Pat. No. 5,109,844 to De Juan, Jr. et al., which include arrays of electrodes coupled to nerve cells of a patient's retina, have been shown to be able to restore low resolution visual perception to blind patients.
Other groups have explored simulating sensory perception using tactile and electrical stimulation of sensations outside of the typical visual pathways. For example, a group at the University of Wisconsin has developed an electrode array for electrically stimulating a patient's tongue to generate visual perceptions. Others, for example, at the University of Arizona, Tuscon have explored inducing visual perceptions through tactile stimulation of the skin.
While current implant technology has been demonstrated to stimulate some amount of visual perception, each visual prosthesis needs to be trained for its individual patient in order to effectively elicit the appropriate visual perception. Prime candidates for visual prostheses are previously sighted individuals who have had their normal visual nerve activity damaged by various conditions, for example macular degeneration or retinitis pigmentosa. However, due to the visual damage in such candidates, predicting in advance the perception induced by a visual prosthesis in a particular candidate has proven difficult.